Your best bet would probably be to use Body.ApplyForce on every body within the radius of the explosion in the direction opposite it - most likely with some sort of falloff over the distance from the center of the explosion. That would look something like
this:

As for animating the explosion, I'd suggest using an explosion generator like
Explogen (try the first download link, for some reason the second one didn't work on my computer). A slightly less user-friendly alternative is
Positech's Explosion Generator.